Process of making bimetal thermostatic elements



Aug. 24, 1943. T. B. CHACE 2,327,500

PRQCESS OF MAKING BIMETAL THERMOSTATIC ELEMENTS Original Filed May22,1936

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2720722095 3, Zac e l Patented Aug, 24, 1943 s. PATENT OFFICE PROCESS OFMAKING BIMETAL THERMO- STATIO ELEMENTS Thomas B. Chace, Winnetka, 111.,assignor to The Dole Valve Company, Chicago, 111., a corporation ofIllinois Original application May 22, 1936, Serial No. 81,284. Dividedand this application December 19, 1939, Serial No. 309,977 r 1 Claim.

This invention relates to a process ofmaking thermostatic bimetals. Theinvention has as an object to provide a process of making a thermostaticbimetal which when formed into a thermostatic element, will have auseful deflection with temperature change and will particularly havealso a high tensile strength and a high resistance to set, so that nochange in calibration takes place when the bimetal is incorporated in adevice that after useful deflection takes place and further movement ofthe bimetal is then prevented, the temperature to which the bimetallicelement is subjected continues to rise, building up considerable forcein such element.

Tensile strength or resistance to set, as it applies here, of asolid-solution type alloy is first the result of chemical analysis.Variables of these properties are relative to hardness, .and hardness isrelative to wroughting or work hardening. The present thermostaticapplications require severe forming of the elements to incorporate themin thermostat devices. I have found thatif the now availablethermostatic bimetals are hardened by Working, such as rolling to theextent that resistance to set' is high, they are too refractory andfracture in forming, which fracture becomes the weakest point anddestroys the resistance to set. If work hardened only sufficiently to beductile enough for forming, the resistance to set is low.

The invention has as a further object to provide a heat treating processby means of which thermostatic metal parts are hardened, resulting in anincrease in torque and in the neutralization of the internal strains, sothat the thermostatic element will return to the same position at agiven temperature after repeated heating and cooling thereof.

Invar or the low expanding nickel alloy has a higher modulus ofelasticity than the copper alloys in similar work hardened condition andone object of this invention is to provide a bimetal element of Invarand a copper alloy, which copper alloy has a similar modulus ofelasticity to Invar. The invention may be used in any desired mannerwhere thermostatic metal is desirable.

A particular application of the invention is automobile cooling systemthermostats incorporating a movable valve for controlling waterfiow anda temperature responsive bimetal coil element which is arranged in acoil or otherwise, to move the valve to its open and closed position.For purposes of illustration, -I have indicated in the drawing one formof device illustrating such use.

Fig. 1 is a view in part section, showing an automobile cooling systemwith" a valve and thermostat in position;

Fig. 2 is an enlarged sectional view through the casing of the valve andthermostat;

Fig. 3'is a sectional view through the valve casing, taken on line 3-3of Fig. 2, showing the entire valve. I

Like numerals refer to like parts throughout the several figures.

This application is a division of my application Serial No. 81,284,filed May 22, 1936, which issued March 26, 1940, as U. S. Patent No.2,194,738.

In this construction there is a valve [arranged in a casing la, thevalve and casing being located in the pipe 2 leading from the enginejacket 3 to the radiator 4. I have illustrated a stop 5 which is engagedby the valve when the valve is in its fully open-position, as shown indotted lines in Figs. 1 and 2, When the engine is cold the valve isclosed, as shown in full lines, and when the cooling liquid for theengine heats up, the thermostat is heated and moves the valve to itsopen position. In this use in its action through the temperature rangeof approximately 140 to 180 F., the bimetal element has completed'itsuseful deflection and the valve has reached its wide open position, asshown in dotted lines in the drawing, so no further travel is necessaryor possible. Temperatures greatly in excess of 180 F. are sometimesreached in an automobile cooling system due to low water, frozenradiator, or numerous other causes. Any increase in temperature over 180F. builds up a force in the bimetal element, which if free wouldcontinue to deflect with temperature increases. Since the valve i cannotmove any farther than to its fully open position, as shown in dottedlines, its movement is stopped and the increase in temperature simplybuilds up a force in this thermostatic element without producing anyfurther movement of the valve I. If the element does not have a highresistance to set, under this condition a change in calibration takesplace increasing the operating range above the original to F., causingcontinual overheating and possible severe damage to the engine.

I have provided a thermostatic bimetal entirely satisfactory for thistype of application by utilizing with a low expanding member, suchmember formed of nickel and iron' containing 32 to 45 percent nickel andremainder iron, at

series of copper alloys having relatively high and cooperatingco-eificients of expansion and other properties permitting a combinationof the nickel steel alloy and one of the copper alloys of approximatelyequal proportional thickness in composite slab form to be converted intosheet form. These copper alloys have the important property of hardeningwithout working or reduction of area so that the completely formedbimetal element as ready for assembly into the device can be furtherhardened and resistance to set increased by aging.

I provide a copper alloy, which of the solid solution type, has arelatively high modulus of elasticity and to thi I add an element orcombination of elements, the solubility of which in the copper alloy isgreater at high temperatures than at low temperatures,

Age hardening, or precipitation hardening occurs only in alloys of thesolid solution type which contain a hardening constituent, thesolubility of which in the alloy at high temperatures is greater than atlow temperatures. The solid solution when quenched from the above solidsolubility temperature is supersaturated and unstable and on reheatingto a temperature below the solid solubility temperature, the unstablesolution tends to revert to an equilibrium condition which correspondwith a tempering effect. The resulting increase in hardness is asupersaturated solid solution hardening.

Usually increase in hardness and strength or resistance to set arecomparable and this is true of the alloys covered here for thermostaticbimetal, although there are some exceptions to the rule.

There is a change with temperature in the solubility of iron in copperfrom approximately 4 percent at 2000 F. to approximately .5 percent at1000 F. I find that iron as a hardening constitutent in my copper alloyfor thermostatic metal use to be particularly desirable, as drasticquenching is not necessary to bring about supersaturation at lowtemperatures. Remarkable hardening can be produced by cooling slowly andreheating to a temperature under the first temperature. The Solubilityof silicon in copper varies from 6.7 percent at 1350 F. to about 4percent at 750 F. but a copper alloy containing over 3 percent siliconis very refractory and difficult to roll. So silicon alone as ahardening constituent is not desirable. However, silicon with necessaryamounts of nickel, iron, chromium, or cobalt forming the correspondingsilicides are particularly susceptible to age hardening; for eX ample,nickel silicide is soluble in copper to the extent of 8.2 percent at1830 F. and only .7

percent at 570 F. Cobalt silicide is soluble in copper to the extent of3.3 percent at 1830 F. and only .7 percent at 570 F. I have found that anickel-iron-silicon-copper alloy having the metals in substantially thefollowing proportions to be particularly useful and eilicient for mythermostatic bimetal, nickel .5 percent to 5 percent, iron .1 percent to5 percent, silicon .5 percent to 3 percent, and the remainder copper. Imay add to the foregoing materials manganese in the proportions of .25percent to 1 percent. I may also use the following alloy, for example,silicon .5 percent to 1 percent, cobalt .5 percent to 3.5 percent, andthe remainder copper, or I may use silicon .5 percent to 1.5 percent,nickel .5 percent to 5 percent, iron .1 percent to 5 percent andaluminum .5 percent to 5 percent, and the reing temperature.

mainder copper, or silicon .3 percent to 3 percent, nickel 2 percent to30 percent, aluminum .5 percent to 8 percent, and the remainder copper.Other alloys which I may use may be as follows.

.5 to 15% Mn, 5 to 10% Al, remainder Cu.

.5 to 3.5% 00, 5 to 10% Al, remainder Cu.

1 to 3% hi, 5 to 40% Ni 5 to 10% 5n, remainder Cu. .5 to 3% Si, .25 to5% Ni, remainder Cu.

.5 to 3% Si, .25 to 3.5% ()0, remainder Cu.

.5 to 3% Si, .1 to 5% Ur, remainder Cu.

1 to 3% Si, 2 to l2% Mn, remainder Cu.

1 to 3% Si, 1 to 5% N15 to 35%1411, remainder Cu. .5 to 3% si, 10 Lo 40%Ni, remainder Cu.

1 to 32% Sn, .25 to 2.5% Be, remainder Cu.

.5 to 2% Ni, .25 to 2.5% Be, remainder Cu.

.5 to 3% bi, .l to 5% be, remainder Cu.

.5 to 10% Fe, remainder Cu.

10 to 75% Ni, 1 to 10% Al, remainder Cu.

10 to 70% Ni, 1 to 107 Al, Lu 5% le, remainder Cu.

The thermostatic bimetal of Invar and one of the above copper alloys forthis purpose are welded in slab form and rolled into sheets or strips.This is cut up into usable sizes and then formed into coils or othershapes and then treated to increase resistance to set.

The details of method in obtaining the increased strength or resistanceto set varies with the difierent combinations of copper alloys andnickel-steel, but the resulting strength of the bimetal element aftertreating is greater than that obtained by work hardening as by coldrolling to a hardness which is still ductile enough for forming into acoil shaped like the automobile cooling system thermostatic coil.

Hardening of an age hardenable alloy is done by heating to approximatelythe solid solution temperature of the particular alloy and thenquenching. The hardening or aging takes place during a subsequentreheating of one to several hours to a temperature lower than thequenchlhe quenching temperature is usually between 1300 F. and 1600 F.and the aging temperature between 400 F. and 1150 F. When temperatureand time prior to quenching are sufilcient to anneal or soften theInvar, the following increase in hardness by aging the copper alloywould in some combination not be as great as the loss and the bimetalshape would have a lowe resistance to set than before age hardening. Inthis event, the first heating and quenching is done prior to thefinished gauge thickness and then cold worked by rolling to harden theInvar, which work hardens more readily than the copper alloy. The copperalloy is partially hardened by the cold working but only suificiently soas to be ductile enough for forming. Further hardening is thenaccomplished on the formed or shaped individual bimetal coils or piecesby aging at a temperature lower than the quenching temperature. Theresulting increased hardness of the copper alloy is similar to theeffect from excessive cold working but if hardened in sheet form by coldrolling the material would not form, as described, without fracture.

I have found that the preferred heat treatment is a heat treatment at atemperature to bring out the increased enlciency of about 650 F. and thepreferred length of time to be two sixhour cycles of heating at thistemperature and then slowly cooling at room temperature. The desiredresults can be obtained by various combinations of type and temperaturewithin the temperature range of 400 F. to 750 F.

I claim:

The process of making bimetal thermostatic elements, which consists inWelding together a strip of a ferrous alloy comprising 35 percent to 45percent nickel, and a. strip of copper alloy comprising silicon 0.5percent to 3.0 percent,; nickel 0.5 percent to 5.0 percent, manganese.25; percent to 1.0 percent, iron 0.1 percent to 5.0 percent and theremainder copper, quenching at a temperature between 1300 F.and 1600 F.,a portion of the exposed surfaces'of both strips being out of contactand applying pressure to the THOMAS B. CHACE.

3 W sed surfaces of the strips by cold rolling said g a suflicient timeto harden the copper alloy leave it still ductile enough for forminginto a haped thermostat, and then heat treating V strip at a temperaturewithin the temperatur'range of 400 F. to 750 F.

